1. Technical Field
The present invention relates in general to an improved wellhead seal, and in particular to an improved metal-to-metal casing packoff.
2. Description of the Prior Art
In general, prior art casing packoffs typically utilize elastomer seals. Unfortunately, most elastomer seals cannot meet the API PR2 testing for packoffs, as outlined in API 6A, 17th edition, appendix F, without some type of special field machining to the casing. Some packoffs have been of the metal-to-metal sealing type, but again require the casing to be field machined and special sealing tapers in the wellhead housing.
In contrast, the packoff of the present invention combines several sealing features in one assembly to achieve a metal-to-metal primary and cross-over packoff. This packoff meets the API PR2 packoff testing requirements of API 6A, 17th edition, appendix F. In addition, the present invention can be used in high temperature (above 350 degrees F) and high pressure (in excess of 10,000 psi), without the need for special field machining. A packoff constructed in accordance with the present invention is also the primary seal for slip-type casing hangers during service (FIG. 4).
An all-metal seal assembly is located between the exterior of a string of casing and the bore of a lower wellhead housing. The seal assembly has a base seal member with inner and outer legs that define a U-shaped cross-section extending upward into the bore. Each leg is provided with a set of seal bands for sealing against the bore and casing, respectively. When an upper wellhead housing is landed on top of the lower wellhead housing, an energizing ring is forced into the U-shaped cross-section and spreads the legs apart from each other, thereby moving the two sets of seal bands into sealing engagement with the bore and the casing.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.